1. Field of the Invention:
The present invention relates to a water mixing device that mixes hot and cold water at a preset mixing ratio which can be regulated to obtain a desired final water temperature.
2. Description of the Related Art:
An example of such water mixing device as described is disclosed in Japanese Patent Laid-open Publication No. 61-140685 published on June 27, 1986.
The disclosed device includes, as re-illustrated here in FIG. 1 of the accompanying drawings, a hot-water passage 1, a cold-water passage 2, and an automatic pressure regulating valve 3 disposed in connection with the water passages 1, 2. The automatic pressure regulating valve 3 is composed of a hot-water side valve element 4 for reducing the primary pressure in the hot-water passage 1, a hot-water side valve seat 5, a cold-water side valve element 6 for reducing the primary pressure in the cold-water passage 2, a cold-water side valve seat 7, a connecting member or means 8 for interconnecting the hot-water side valve element 4 and the cold-water side valve element 6, and a piston 9 movable in response to a differential pressure created between the primary pressure of hot water and the primary pressure of cold water that have been reduced by the respective valve elements 4, 6. When the pressure of hot water or the pressure of cold water changes suddenly, the automatic pressure regulating valve 3 is immediately responsive to a differential pressure thus created so as to balance the secondary pressure of hot water and the secondary pressure of cold water at all times. Hot water and cold water are mixed with each other at a mixing ratio which can be varied by a temperature regulating valve 12 driven by a motor 11 to regulate the final water temperature. Mixing portion or chamber 13 is where hot water and cold water are mixed. Thereafter, the temperature controlled water is discharged through a power-driven flow regulating shutoff valve 14. The final water temperature is detected by a mixed water temperature detecting means or sensor such as a thermistor 15. At the same time, the flow rate of the temperature-controlled water is detected by a flow rate detecting means or sensor 16. Detected values from the respective sensors 15, 16 are delivered to a control means or unit 18 which in turn controls the operation of the motor 11 and the flow regulating shutoff valve 14 until the detected values become equal to the setting values set by a setting means or setter 17.
The known water mixing device however has various drawbacks as follows.
Since the pressure regulating valve 3 and the temperature regulating valve 12 are independent of each other, the water mixing device is large in size and complicated in construction and further induces a large pressure loss and hence is not suitable for an application in which a large flow rate is a major requirement. If the pressure regulating valve 3 is omitted, the pressure of hot and cold water acts directly on the temperature regulating valve 12. As the water pressure is variable, an excessively large driving force is necessary to operate the temperature regulating valve 12 without being influenced by the change in water pressure. Furthermore, the response of the motor-driven temperature regulating valve 12 is relatively low and therefore a quick temperature adjusting operation is difficult to achieve. When an electric power supply is interrupted, the motor 11 is brought to a halt and the temperature regulating valve 12 is locked in position. In this instance, if the hot water supply temperature rises or, alternatively, if the cold water supply pressure drops, the final water temperature is elevated to an extent that the user may be damaged by excessively heated water. Additionally, manual operation of the known water mixing device is difficult to achieve unless a complicated mechanism is provided.